1. Field Of The Invention
This invention relates to a hydraulic amplifier valve assembly, particularly for a hydraulic brake system in automotive vehicles and is of the type which has a valve housing receiving an axially displaceable amplifier piston and a control plunger displaceably disposed in an axial passage of the amplifier piston. The control plunger is axially displaceable by a reaction piston which is coupled to a brake pedal arrangement and which is guided in the valve housing and sealed by means of a sole ring seal. The amplifier piston projects into the valve housing only with its pedal-side end portion and is sealed relative to the wall of the valve housing by a sole ring seal situated at the entrance of the valve housing. Coupling nipples for a pressure conduit and for a return conduit are arranged in that portion of the amplifier piston which projects at all times from the valve housing.
2. Description Of The Prior Art
A hydraulic amplifier valve assembly as outlined above is disclosed, for example, in German Patent No. 3,037,218.
The greater the number of seals between the axially relatively movable components of a hydraulic amplifier valve assembly, the greater the friction, particularly if the seals are continuously under pressure and are designed for high pressure stresses. Such friction is particularly disadvantageous in case the hydraulic amplifier valve assembly is, by virtue of its asymmetrically arranged control ports, a pressure-unbalanced valve assembly, because the friction in such amplifier valve assemblies is greater than in pressure-balanced amplifier valve assemblies due to the radial displaceability of the control plunger within the amplifier piston. Such pressure-unbalanced amplifier valve assemblies are disclosed, for example, in U.S. Pat. Nos. 4,379,423 and 4,516,470.
Particularly for the purpose of reducing the above-noted friction, German Patent No. 3,037,218 discloses a hydraulic amplifier valve assembly in which the amplifier piston is not surrounded along its entire length by the valve housing in the usual manner, but is surrounded solely about that end portion thereof into which the control plunger is introduced and wherein only a single ring seal exposed to high pressure is provided between the valve housing and the amplifier piston. The conduit coupling nipples for conduits leading to a hydraulic pressure source and to a non-pressurized reservoir are arranged in that part of the amplifier piston which projects from the valve housing. Upon actuation of the brake these conduits are to be shifted axially together with the amplifier piston and should therefore be axially deflectable (for example, flexible).